1. Field of the Invention
The present invention generally relates to an information embedding apparatus, an information embedding method, an information retrieving apparatus, and an information retrieving method. More specifically, the present invention relates to an apparatus and method for embedding information such as sound information and copyright information (watermark information) in compressed image data, and an apparatus and method for retrieving watermark information from compressed image data having watermark information embedded therein.
2. Description of the Background Art
Recently, the digital watermarking technology is increasingly studied in order to protect the copyrights of the multimedia contents such as images and music. The digital watermarking technology is the technology of confidentially recording (embedding) other information such as copyright information (watermark information) in the multimedia contents such as images and music in order to prevent illegal copying and unauthorized use. Particularly for the image data, there is the technology of embedding sound information as watermark information so that the user can enjoy both image and sound when reproducing the media, in addition to the technology of embedding copyright information for the purpose of regulating such illegal copying and unauthorized use.
Information such as copyright information and sound information (watermark information) is embedded in image data that has already been compressed in a JPEG (Joint Photographic Experts Group) or MPEG (Motion Picture Experts Group) format by using an information embedding apparatus as shown in FIG. 31. This operation is conducted as follows: first, the compressed image data is subjected to variable length decoding operation and run length decoding operation by a variable length decoding section 311 and a run length decoding section 312, respectively, to extract a DCT (Discrete Cosine Transform) coefficient. The DCT coefficient thus extracted is temporarily stored in a coefficient memory 313. An embedding section 314 then embeds watermark information in a bit of the DCT coefficient stored in the coefficient memory 313 based on bit designation information. The DCT coefficient having the watermark information embedded therein is then subjected to run length encoding operation and variable length encoding operation in a run length encoding section 315 and a variable length encoding section 316, respectively. The watermark information is thus embedded in the compressed image data.
As described above, in order to embed watermark information in image data that has already been compressed in a JPEG or MPEG format, the compressed image data is subjected to operations such as variable length decoding, run length decoding, embedding of the watermark information, run length encoding and variable length encoding. However, the information embedding apparatus of FIG. 31 uses a common code table 317 for the variable length encoding operation and the variable length decoding operation, and therefore cannot conduct these operations simultaneously. Accordingly, the DCT coefficient obtained by the variable length decoding operation and the run length decoding operation is temporarily stored in the coefficient memory 313. In this way, the variable length decoding operation of the compressed image data and the variable length encoding operation of the data having the watermark information embedded therein are conducted in a time-sharing manner.